1. Field of the Invention
The present invention concerns a bucket excavator such as a trench hoe with an arrangement for checking the position of its digging device relative to a digging floor.
The invention is particularly applicable to an excavator which carries a deep digging bucket or dipper on its digging device, whose cutting edge corresponds at least to a part of the cross-sectional line of a ditch, so that half-round digging or ditch floors can be produced with such an excavator in one or more operations. Preferably such an excavator is provided with a parallel guidance of its bucket, which once the cutting angle is set, guides the bucket substantially over the entire prospecting range during the digging movement (e.g. along an embankment or an inclined or plane ditch floor) without any special intervention by the bucket operator.
2. Description of the Prior Art
Such excavators already belong to the state-of-the-art (German Pat. No. 1,800,045 and U.S. Pat. Nos. 3,586,182 and 3,656,640). In principle, they are so designed that the hydraulic cylinder for turning the bucket engages, on the one hand, the boom close to the pivot of the dipper arm and, on the other hand, a triangular shift lever secured in the dipper arm next to the pivot of the bucket, and that the shift lever is so connected with the bucket over a short guide rod that the bucket arm, the shift lever, and the hydraulic cylinder together with the front end of the boom form a large four-bar linkage, which is coupled over a shift triangle, formed of the triangular shift lever, with a small four-bar linkage formed of the shift lever, the end of the bucket arm, the bucket and the short guide rod, and that with a given length of the dipper arm and a given length of the boom, the dimensions of the four-bar linkages as well as of the shift triangle are so tuned to each other, and that the large four-bar linkage is so varied by means of the hydraulic cylinder when adjusting the cutting angle of the bucket to the inclination of a slope to be worked on and thus adapted to the inclination of the slope, that the bucket is guided parallel substantially over the entire swing of the bucket during the digging movement, taking into account the swinging movement of the boom corresponding to the inclination of the slope. This has the advantage that the preselected cutting angle is positively maintained, so that the excavator operator only has to actuate the digging movement with a hydraulic cylinder on the digging device of the excavator.
The invention is based on a known excavator of this type, which is provided additionally with a device for indicating the position of its bucket. In the known excavators, a pointer is used which follows a guide rod representing a connection between the swivel hinge of the bucket and an parallel axis base-swivel joint on the pivotal substructure of the excavator. The position indicator can be corrected for inclined positions of the excavator in the guide rod plane on the pointer scale and for different distances of the excavator from the working plane by vertical adjustment of the parallel axis swivel joint on the superstructure of the excavator. Such an arrangement has the following advantage: when the excavator rests, for example, on the crest of a bank, and the slope is to be reworked with a given angle of inclination, the excavator operator only has to change the cutting angle on a part of the slope until the pointer bears on the given slope angle. The excavator operator can then drive the slope from the selected location of the excavator without visual control of the digging device or of the bucket, and correct the cutting angle, if necessary, according to the indication. Such an arrangement ensures the driving of the plane or weakly inclined digging level, but is not suitable for certain specific cases.
For example, this prior art arrangement is unsatisfactory for the driving up of ditch floors with exact maintenance of the given contour of the ditch. This is required in the laying of large pipes of steel concrete, because the ditch floor must be driven corresponding to the curvature of the pipes and corresponding to the gradient of the line consisting of the pipes in order to avoid correction of the pipes. In order to facilitate understanding, the invention will hereinafter be described by the example of such excavating operations. If a excavator is to drive such ditches, it must be driven relatively frequently in a previously dug outer ditch. Since the known arrangement uses the standing plane of the excavator as a reference plane, while the excavator changes its standing plane before and after the driving, it would be necessary in such operations to readjust the measuring arrangement after each driving of the excavator.
It is also known to use laser systems for the optical reproduction of the vertical and horizontal aspects on construction sites. This possibility is based on the sharp focusing of the laser light which is emitted from a suitable transmitter and which forms a clearly visible, e.g. red, cord-like beam. With a suitable target, it is possible to locate a terrain point by means of the laser beam. Such targets are available in different forms, but require as a rule that the laser transmitter be arranged behind the viewer. In some cases, however, (e.g. in narrow outer ditches), this is not possible, or is possible only with expensive auxiliary devices, because the excavator substantially fills the available free space. In addition, a helper must be available to indicate to the excavator operator the parts of the ditch floor to be corrected. This solution is unsatifactory, apart from the required personnel, because reworking of the digging floor does not lead to the required accuracy of the ditch floor, as is necessary, for example, in the laying of large pipes.